1. Field of the Invention
The present invention relates to the packaging of one or more integrated circuits in a single detachable module and refrigeration systems for cooling the same to substantial subambient temperatures.
2. Description of Related Art
It has been recognized for a number of years that the upper limits on the operating speed of digital circuits is temperature dependent, with such circuits having the capability of operating at higher speeds at reduced temperatures. To this end, various techniques have been used to cool the central processing unit of computers so that a higher clock speed may be used. These techniques generally differ substantially from the more conventional cooling techniques of free and forced convection cooling using ambient air, which techniques are normally used to avoid failure of the circuitry due to overheating and/or to allow higher ambient temperature operating conditions without failure of the circuitry.
One method of cooling a central processing unit of a computer is to immerse the same in a liquified gas such as liquid nitrogen. This has the advantage of cooling the unit to a very low (cryogenic) temperature, allowing a very substantial increase in the operating speed thereof. It also has the advantage of good heat transfer between the central processing unit and the cooling medium, which is advantageous for central processing units having a high heat dissipation per unit volume occupied thereby. Such cooling techniques have substantial disadvantages however, in that liquified gasses are difficult to store and must be frequently replenished. They are also bulky and expensive, and thus heretofore generally only used for large computer systems. Such cooling techniques have not generally been used for smaller computer systems, including desk-top and desk-side systems such as work stations and personal computers, because of the more casual, often less frequent use thereof and the greater relative difficulties of providing and maintaining liquified gasses for any period of time in such small quantities.
Solid state coolers, utilizing the Peltier effect have been considered for cooling the central processing unit of desk-top computers. However, these devices are too inefficient to cool the relatively large amounts of heat generated by present and future high speed CPU's. Such coolers demand very large power supplies which add substantially to the cost and bulk of the computer. Furthermore, inadequate consideration has been given to packaging the semiconductor chips for reliable operation at sub-ambient temperatures, where condensed moisture may effect the long term reliability of the CPU.
Closed cycle mechanical refrigerators have also been considered for cooling CPU's to sub-ambient temperatures. These may include freon refrigerators using the Rankine thermodynamic cycle, coolers utilizing the Joule-Thompson effect, and other mechanical refrigerators. In general, these refrigerators require large and bulky compressors, or large, heavy motors which are incompatible with the space requirements for desk-top and desk-side computers. In addition, these refrigerators utilize gears, bushings, bearings, mechanical linkages, and other moving components which wear over time, requiring the use of oil reservoirs and lubricants, which degrade with extended use and under severe operating conditions. Furthermore, most of these systems lack hermaticity, resulting in leakage of the cooling fluid, or diffusion of impurities into the cooling fluid. Consequently, mechanical refrigerators have acquired a reputation for unacceptable reliability for applications in PC and workstation markets.